Question

answer with full expalnation please fast...​

Answer 1

8 cos^3(π/9) - 6 cos(π/9)

we know that

4cos^3A = 3 cosA + cos3A

2*(4cos^3(π/9) - 6cos(π/9)

= 2*(3cos(π/9) + 2*cos(3*π/9) - 6 cos(π/9)

= 6 cos(π/9) + 2* cos(π/3) - 6 cos(π/9)

= 2*cos(π/3)

= 2*1/2

= 1

proved